Multistation duplex system



1953 R. c. CHEEK ET AL MULTISTATION DUPLEX SYSTEM 2 SHEETSY-SHEET 1 Filed Jan. 14, 1949 .E EmcPc.

B Euc- I ma 0| 3330a 23am 33am I Bzooom Fl H wnmzssss: fltw INVENTORS Paul L. Newbury 8 Robert 6. Check.

ATTORNEY Jan. 20, 1953 Filed Jan. 14, 1949 Receiver Code Signal Attenuator WITNESS Receiver Power Supply R. C. CHEEK ET AL MULTISTATION DUPLEX SYSTEM Recelver Oscillator OSCIIICHOY Fig.2.

Transmitter 2 SHEETS-SHEET 2 Transmitter pp y Transmitter 2 INVENTORS Paul L'. Newbury 8 Robert O. Cheek.

ATTORNEY Patented Jan. 20, 1953 Robert 0. Check, Irwin, Pa andz-Paul L. Newbury, East Aurora,- N. -Y,, assignors to Westinghouse Electric "Corporation, East .Rittsburgh; Pa., a corporation of Pennsylvania.

Application January 14, 1949,-Seria1 No.' -'Z0;854

=16 Claims.

Our. invention. relates .to communication apparatuspand it has-particular relation. to multistation, point toepoint, :two-way communication :sets.

Eaoh station of a.multi-station,ttwoway,parrier :communication system :includes two transmitters designed to operate .at :diiierent trequencies =anditwo receivers designed :to operate at the same' frequencies. 'Inathequiescentrstate. each station is set to:receive one zfrequency,.say F1, and to transmit the other frequency '32. AA stationabout to callianother station :is converted to transmit-on frequency E2 and receiveon sirequency P1.

In such two-way .carrier current communica- :tion systems, therreceiving stationmustioe prop- :erlyset up for reception. Among other :items, theoperator must be notified of the incomingcall .and the receiving frequency. F2 must be maintained. In .a communication system .in -.which the carrier is transmitted, this setting :upiunc- .tion may be .performedefiectively by :the :un-

modulated carrier.

In .recent times, single .side bancl'suppressed carrier transmission .has .been awide1y...adopted for two-way carrier current communication systems. v.In such systems, .the iunmodulated :car- .rieris not transmitted, and "is not available-to perform the setting :up .;function. There .amay,

moreover, :loe communication systemsin the -.op-

eration .of which/the ,unmodulated .carrienis transmitted but, .for :one reason or another, .can- .notconveniently paused ,for setting up.

It is, accordingly, :broadly an object .of .our

invention to :providepina two-Way carrier current .communicationsystem control apparatus ,for setting ;up.the receiving stations; to .receive a call.

Another obj eot .Qf ourpinvention is to ,pro.vi d e a single (or double) side-band, suppressed carrier, carrier current communicationsystem in which each of the stations shall .be provided with control apparatus iorsetting upa remote station for reception.

,A more specificobjectof ourinventiongis to. provide a single or doubleside-band, amplitude modulated .multi-station, carrier-current .communication system of the duplex typein which the independent stations .shall include control .apparatus for setting up remotestations for reception independently of any carrier.

Another specific object-of our iHVBII DiOHfiS to providein a two-way communication system of the duplex type control apparatus in each station for providing a ringing signal 'at a remote tion transmits a codesignal.

zstationend o s t n up t -transmitters and ;;receivers of each. of..-the stations for 1, communication.

;-In accordance with .our -invention, we provide aduplex communication-system in which a:trans .ifer relay is provided ateach station .for-selecting for operation one-.of a ;pair of transmitters .de-

si e t sen a different r quen i s. say :-:F

nd F2,1B4 ld'Dne oi a pairiof.receiverszdesigned to receive at the same freg1uencies.. .In-.t he

quiescent .state, all stations are. set Etmselld at one of the i edu n ies. ay andreceive a the other F2. When. acstation :is -to..transmit, the operator causes the transfer relay to be actuated todisable the transmitter and receiver set for transmissionand reception in .the quiescent state and enable theeother transmitter .and

receiver. .Once so set up, the transmitting .sta-

The code signal causes a -bell {to ring .and-actuates-.a switching :meohanism ,to block: operation of the transfer relay at the remote station. -When theoperator at the remote station hears the -r1ng sand picks up his instrument, the, remote station is locked in ior communication. .The sending station is .locked in for communicationwhen its .operatorpiclzs up his in trument.

The novel features that we ..consider :phar- .acteristic of.-our invention, are set iorth-withgparticularity in :the appended claims. The.;.inven tion itself, :however, both as-.- to its organ zation and method of operation, together with -1a,ddi-

tional ob ects and advantages thereof, .,will best -he understood from the.following.descriptign-.of

a specinc em diment wh mea in o ect o with t ompany ng,draw ngs, r-i WhiQh .IIi ure ,1 is ap r u t diae am 3a t pic station of a duple s n le side-.bandflhnmssfi .Garrier... c9 11l lQ8l sy tem .i a cordan with our nv ntioman Fig. -2 is. a circui di g am o a othe statio of this communication system.

The station shown in Figure 1 includes agreceiver 3 designed to operate at 311 frequencyjFl and a second-receiver -5 designedto operate at a' frequency F2. Eaeh'receiverds designed to receive the modulated carrier frequency" which may be designated Fla-Fm or FZ-FFmdassuming that the upper side-band is transmitted). Each=reoeiver includes :a local oscillator which 'may have a "frequency Fl-l-Fi I Q I FZ-l-Fi for the other. A power supply I -'i's--profor one "and vided for energizing receivers 'FLand'FZ. "The power supply *1 may-be app1ied-to receiverfFl, or

T2, through --the-contacts 0P9 or H respectively of a transfer relay I3, in dependence upon the position of this relay. In the quiescent state of the station. the relay I3 is deenergized and the power supply I is connected to energize receiver Fl.

The station also includes a pair of oscillators I1 and I9 tuned to frequencies F1 and F2 respectively. These oscillators may be connected to a mixer I5 through contacts 2I and 23 of the relay I3. With the relay deenergized oscillator Fl is connected to, and oscillator F2 is disconnected from the mixer l5. The mixer I5 is connected at one of its terminals 21 to the local oscillators of receivers FI and F2 and receives from these oscillations of frequency F1+Fi or FZ-I-Fz'. The output terminal 25 of the mixer I5 is connected to a demodulator 29 and supplies to it oscillations of frequency Fi. Frequency Fi-I-Fm is derived at the outputs of the receivers FI and F2. This output may be connected to the demodulator 29 through contacts 3l and 33 of the relay I3. In the quiescent state of the station receiver 3 is connected to, and receiver 5 is disconnected from,

the demodulator. The demodulator converts the 'signals supplied to an audio signal of frequency 'Fm. One branch of the output of the demodulator 29 is connected to a code signal attachment 35 and the other branch through an audio hybrid =31 to the sound-electric energy conversion instrument'39 of the station.

The station also includes a pair of transmitter output amplifiers; one II) designed to operate at frequency F1 and the other (43) at frequency "F2. One or the other of these transmitters may be connected to a power supply 45 through contacts 41 and 49 of the relay I3 and in the quiescent setting of the station transmitter F2 is connected and transmitter Fl is disconnected. In dependence upon the setting of the transfer relay 53, one or the other of the transmitter amplifiers 4| or 43 is connected to receive the output of a modulator 50. This modulator is supplied from -the output of the oscillators Fl or F2, I! or I9, through contacts 5I or 52 respectively, in de- "pendence upon the setting of the transfer relay. -With the transfer relay in the deenergized condition, when the station is quiescent, the modulator 50 is connected to the oscillator F2 through a normally closed contact 53; it may be connectedto the transmitter Fl through another "contactor 55 when the relay The output of an audio amplifier 51 may be connected to the modulator 59 through a normally open contact 59 of a relay 6| which is ac- --tuated to lock in the system for communication I3 is energized.

by removal of the instrument 39 from its support I 63. "Theaudio amplifier 59 is connected to the instrument 39 through the audio hybrid 3'I.' The "input of the modulator 59 may also be connected to a generator 65 which produces a signal for operating the bell at a remote station through normally open contact 91 of a relay 69 which is actuated when a call is being initiated.

separate antennas must be provided. 7

The station shown in Fig. 2 is similarly provided with receivers Fl and F2, I5 and 1! respectively, a power supply I9, a mixer 8I, a demodulator 83, and a code signal attachment 85 common to the receivers. The station shown in Fig. 2 also includes oscillators FI and F2, 8! and 89 respectively, transmitter amplifiers Fl and F2, 9| and 93 respectively, and a power supply 95 for these amplifiers. The inputs of the receivers Fl and F2, and the outputs of the transmitters Fl and F2 are connected to the power line I3 through a resonant network 97. The station shown in Fig. 2 is further provided with a common modulator 99, and audio hybrid NH and an audio amplifier I83. It includes a ringing modulation generator I05 and associated relays I31 and I09 as at the Fig. 1 station. There is also a transfer relay III which is deenergized in the quiescent state of the station so that receiver Fl is set for receiving and transmitter F2 is set for sending.

Each of the stations also includes a synchronous timer Il3 and H5 respectively which is energized from an alternating power supply II! and H9 respectively. This timer may be a clock mechanism or an electronic timer. Initially, the operating contact I2I and I23 of the timer II3 and H5 is open. When power is supp-lied to a station, for example the station shown in Fig. 1, a circuit is closed which extends from a terminal of the alternating current supply II'I, through normally closed contacts I35 of a relay I33, the operating coil of the timer II3, normally closed contacts I28 of slow drop-out relay I3I, normally closed contacts 231 of double coil relay 23I to the other terminal of supply I I1. When, after a time delay, the operating contact I2I of the timer II3 closes, a circuit is closed which extends from a positive terminal of a direct current supply I25 through a conductor I27, normally closed contacts I29 of a slow drop-out relay I3I, the timer contact I2I, the exciting coil of a relay I33, which when deenergized blocks operation of the transfer relay I3 to the negative terminal of the supply I25. The blocking relay I33 is actuated and at one of its contacts I35 now opens to the energizing circuit for the timer H3. The timer is deenergized, and its operating contact I2I opens. The blocking relay I33 remains energized through a lock-in contact I31 which is now closed. At the station shown in Fig. 2 a blocking relay I39 is similarly actuated.

In Figs. 1 and 2, several of the components such as the receivers, transmitters, power supply and oscillators are represented by blocks 3, 5, "I,

I5, l1, 19, ill, 43, 45, 9|, 93, 95, I1, I981, 89, 29, 83, 35, 85, 31, IIII, 50, 99, 51, I83. The blocks are used to simplify and shorten the description of the apparatus. Components corresponding to the blocks are shown in detail in the following publications:

ReceiverWestinghouse leaflet I. B. 84-797-1A, dated September 1, 1948, entitled Single Side Band Receiver.

Transmitter-Westinghouse leaflet I. B. 84-796- lA, dated November 1, 1948, entitled Single Side Band Transmitters.

Modulator, demodulator, mixer and oscillator- Westinghouse leaflet I. B. 84-795-1A, dated November 1, 1948, entitled Single Side Band Units.

Code signal attachmentWestinghouse leaflet 84-755, dated January 1946, entitled Code Signal Attachment.

Audio hybr1d'Westinghouse leaflet 84-751, dated January 1946, entitled Audio Hybrid.

7 Let us assume that the operator, at the station aces-sic 5. shown in Fig. 1, desires 'tocommunicate with the operator at the station shown in Fig. 2. The former then actuates a hand-generator I4I-causing current to flow from one terminal of the hand generator through a normally closed contact I43 of a slow drop-out relay I45, a capacitor I ll, a rectifier I49, the coil of the initiating relay 69, another normally closed contact -l5I of the slow relay IE5, to the other terminal of the hand generator. The initiating relay 89 picks up. At one of the now open contacts I53 of this relay, the circuit between the'audio hybrid 37 and the hand generator MI is opened so that the ringing voltage from hand generator l ll will not be impressed upon the audio amplifier 5'! through audio hybrid 3?. At another of the now closed contacts I57 of the initiating relay 69, a circuit is closed which extends from one'terminal of a directcurrent supply I25 through the coil of a slow dropout relay I59 to the other terminal. This latter relay is now actuated, closing at its now closed contact ilil, a circuit-from'the alternating power supply I I? through the exciting coil of the transfer relay I3. The transfer relay I3 is thenactuated, disconnecting receiver Fl from the power supply I and the demodulator 29, oscillator Fl from the mixer I 5, transmitter F2 from the power supply ie, and oscillator F2 from the modulator '59 and connecting receiver F2 to the power supply and the modulator 2e, oscillator F2 to'the mixer l5, oscillator F I to the modulator 5B, and transmitter Fl to the power-supply A5. The slowrelease relay continues to hold closed the circuit through the exciting coil of the transfer relay I3 after the operation of the hand generator stops. The operator at the'sending station turns the hand generator I i-I on and off for short and long intervals in accordance with a pre-established code system The number and sequence of these intervals identify the desired receiving station. As the hand generator is turned on and 01f, the initiating relay is energized and deenergized and its contacts are opened and closed. However, the slow relay I59 and the transfer relay I3 remain actuated throughout.

When the initiatingrelay 69 is energized at the sending station, it also closes the contacts 6'1 which connect the ringing modulation generator 65 to the modulator 50. The ringing code is, therefore, transmitted .by transmitter Fl. Receiver Fl (75) at the receiving station receives this code signalandatthe output of the receiving code signal attachment 85 aseries of long and short pulses are produced. .A relay I63. at the output of the attachment 85 is actuated re- .peatedly for long or .short intervals in accordance with the code. Atanow closed contact I65 of this code relay I63, a circuit through the exciting coil of a slow drop-out relay It] is closed.

At now open contacts I69 and I'll of this slow relay ISl, and now closed contacts Iti, the telephone line I82 is transferred from the audio hybrid Ilil to the source of ringing power I84. The circuit fromthe hand generator ITII through the initiating relay IE9 at the receiving station is also opened. The operator at the receiving station cannot, therefore, energize his initiating relay I69 by actuating the hand generator Ill. Since the initiating relay I09 cannot be energized, the circuit through its normally open contact I13 and the coil of the slow-acting relay I15 which controls the transfer relay III cannot be closed. For the time being, therefore, the transfer relay l I I-cannot be actuatedand the receiving 6; station is set to receive signals transmitted on frequency F1.

The energizing circuit for the bell I89- at the receiving station is closed at a pair of 'now'closed contacts I8l of the slow relay I61, and the bell rings. The slow relay I6! is energized and-deenergized for long and'short intervals in accordance with the code sent and a sequence o'f'long and short rings are produced.

At another now closed contact I83 of the code relay IE3 at the receiver station, 'a circuit is closed which extends from the positive-terminal of a power supply I85 through a normallyclosed contact It'll of the initiating relay Ma a normally closed contact [89 0f the relay 101, which when energized locks in the system for sending, the now closed contact I83 of the code -relay l63, and the exciting coil of the first relay I91 -of a relay chain. The firstchain relayl fil is actuated; at its now closed contact I93, closes-apircuit from the positiveterminal of the supply I85 through the exciting coil of an auxiliary slow drop-out relay I95 of the chain. At a now closed contact I9? of the slow relay I955, a circuit is closed through the exciting coil of a wigglestick relay I99 of the chain. Through one of the repeatedly closing contacts ZIll, of the wigglestick relay, a circuit is closed through the exciting coil of a second slow drop-outrelay 263 of the chain. At its now closed contact-ilili, thisslow relay 2553 is locked inthrough theother repeatedly closing contact'2ifi of the wiggle-stick relay its so long as the movable contact of thelatter continues to vibrate. At a now open contact 209 of the second slow relay 203, the lock-incircuit for the blocking relay I39 is broken. The relay chain I9i, I95, I99 and 2&3 maintains this circuit through the exciting coil of the blocking relay I39 open continuously while the bell rings .and independently of the discontinuity of the code.

At a now open contact 2H) of .theslow relay 293 the circuit through the timer II5 .is maintained open. The timing operation of the timer cannot start, therefore, untilafter slow relay 203 isdeenergized, that is, after the'ringing stops.

When the blocking relay is deenergized, .its lock-in contact 2 opens; its normally .closed contact 2I3 in series with the timer .closes, and its contact-H5 in series with the coilof the slow acting relay I15 which controls the transfer relay III is opened. The slowrelaylflecannot therefore be energized through this contact 2I5. After the transmission of the code signal stops, the chain of relays I9I, I95, I99, 283 is also deenergized and the normally closed contact 2W 0f the second auxiliary slow relay 2ll3inseries withthe timer H5 is closed. Since contact 2I3 of the blocking relay is closed the timer circuit now begins its timing operation. This operation continues from 5 to 45. seconds and after the time interval, the timer contact I23 closes, reenergizing the blocking relay I39 unless the receiving operator has removed his instrument Ilii from its support EN.

The operator at the transmitting stationcontinues to operate his hand generator I4I intermittently and to ring the bell I80 at the receiving station intermittently. After he has actuated the hand generator at least through one complete code, the operator at the transmitting station removes his instrument 39 from its support 63. The removal of the instrument 39 closes one circuit through the mouthpiece mechanism 2 I 9,, and the primary 22I of an audio transformer and a second. circuit through the earpiece mechanism 223 and the secondary 225 of this'transformer. The operator at the sending station may now speak into, and receive speech through, his instrument 39.

Through another contact 221 of the instrument support 63, a circuit is closed which extends from one terminal of a direct current supply 229 through the exciting coils of a double coil relay 23I, a conductor233, the contact 221 to the supply. Through a now closed contact member 235 of this relay 23I and the contact 221, a second circuit is closed through the exciting coil of the communication lock-in relay BI. At a, now open contact 231 of the double coil relay 23I, the circuit through the sending station timer H3 is opened and timing operation of the timer is prevented.

At a now open contact 239 of the lock-in relay 6| 2. second open gap is produced in the circuit through the exciting coil of the first rela; 2M of the relay chain at the sending station. Operation of this relay 2M by code signals which may be received accidentally is, therefore, prevented.

At a now closed contact 243 of the lock-in relay 9|, a circuit is closed which extends from the source I25, through the normally closed contact 235 of the initiation relay 69 which is now deenergized, the now closed contact 243 of the lock-in relay, the still closed contact 241 of the still actuated blocking relay I33, the exciting coil of the slow relay I59 which controls the transfer relay I3 to the supply. The slow relay I59 is now locked in its energized condition so long as the instrument 39 remains removed from its support.

Because the slow relay I59 is not immediately releasable, the transfer relay I3 remains energized for the short time interval between the actuation of the hand generator and the removal of the instrument 39 from its support 63. However, even if the transfer relay should be deenergized by drop-out of the slow relay before removal of the instrument 39, the transfer relay would be reclosed by actuation of the lock-in relay BI and subsequent reactuation of the slow relay I59.

At the now closed contact 59 of the lock-in relay-6|, the audio amplifier 51 is connected to the modulator 59. The signal from the secondary of the audio output transformer 22I225 when the operator speaks, now flows through the hybrid 31 and the audio amplifier 51 to the modulator 50 and is transmitted at frequency F1.

At the receiving station, the operator on hearing his bell I89 removes his instrument I19 from its support 2I1. He performs this act before the timer II has been actuated and relay I39 has been reenergized. If he does not, the calling operator continues to operate his hand generator I4I thus maintaining the receiving station in condition for reception until the instrument I19 is picked up within the timing interval. The circuits through the receiving station audio transformer 249 and the mouthpiece and earpiece mechanisms 25l and 253, respectively, are closed in the same manner as at the sending station. In the same manner as at the sending station, a circuit is also closed through the exciting coils of a double coil relay 255 and a lockin relay I91 is energized. At the now open contact 259 of the double coil relay 255 the circuit through the timer H5 is opened. The timer does not, therefore, close its contact I23 to actuate blocking relay I39 so long as the receiving instrument I19 is removed from its support 2I1. The closing of the contact 26I of the lock-in relay I91 in series with the coil of the slow relay does not, therefore, cause a circuit to be closed through the slow relay and the transfer relay remains unenergized. The receiving station continues to be set at receiving frequency F1 and transmitting frequency F2. Since the lock-in relay is actuated, the audio amplifier I93 is connected to the modulator 99 and the speech of the operator at the receiving station can transmit at frequency F2.

The sending station may be re-set for calling or receiving by the replacement of the instrument 39 in its support 63. Under such circumstances, the lock-in relay 6| is deenergized and both the slow-release and the associated transfer relays I59 and I3, respectively, are deenergized.

When the instrument. I19 at the receiving station is replaced on its support 2I1 the double coil and lock-in relays 255 and I01 are deenergized, contact 259 recloses, the timer II5 times out and blocking relay I39 is reset. The receiving station may now call or receive.

While we have shown and described a specific embodiment of our invention, we are fully aware that many modifications thereof are possible. Our invention, therefore, is not to be restricted except insofar as is necessitated by the prior art and by the spirit of the appended claims.

We claim as our invention:

1. A communication set including a first single side band transmitter designed to operate at a frequency F1 and to transmit a side band only at said frequency F1, a second single side band transmitter designed to operate at a frequency F2 which differs from the frequency F1 and to transmit a side band only at said frequency F2, a first receiver designed to operate at said frequency F2, a second receiver designed to operate at said frequency F2, standby connections enabling receiver FI and transmitter F2 and disabling receiver F2 and transmitter FI, and connections responsive to a locally generated signal for disabling receiver FI and transmitter F2 and for enabling receiver F2 and. transmitter Fl.

2. A communication set comprising an instrument for effecting a conversion between sound and electric energy, a support for said instrument, a single side band receiver designed to operate at a frequency Fl, another single side band receiver designed to operate at a'frequency F2 which differs from Fl, 2. single side band transmitter designed to operate at said frequency Fl, another single side band transmitter designed to operate at said frequency F2, first connections for enabling said F1 receiver and said F2 transmitter and disabling said F2 receiver and said Fl transmitter, means for producing locally a signal while said instrument is on said support, second connections responsive to said locally produced signal for disabling receiver FI and transmitter F2 and for enabling receiver F2 and transmitter Fl so long as said signal is being produced and while said instrument remains on said support, and third connections responsive to the removal of said instrument from said support, for maintaining said Fl receiver and F2 transmitter disabled and said F2 receiver and F1 transmitter enabled after said signal has been interrupted and so long as said instrument remains removed from said support.

3. A communication set including a first single side band transmitter designed to operate at a frequency F1, a second single side band transmitter designed to operate at a frequency F2 which differs from the frequency F1, a first single side band receiver designed to operate at said frequency F1, a second single side band receiver designed to operate at said frequency F2, standby connections enabling receiver Fl and transmitter F2 and disabling receiver F2 and transmitter Fl, and connections responsive to a locally generated signal for disabling receiver Fl and transmitter F2 and for enabling receiver F2 and transmitter Fl and for causing said F1 transmitter to transmit a second signal.

4. A communication set comprising an instrument for effecting a conversion between sound and electric energy, a support for said instrument, a single side band receiver designed to operate at a frequency F1, another single side band receiver designed to operate at a frequency F2 which differs from F1, a single side band transmitter designed to operate at said frequency F1, another single side band transmitter designed to operate at said frequency F2, first connections for enabling said F1 receiver and said F2 transmitter and disabling said F2 receiver, and said F1 transmitter, second connections responsive to a locally produced signal for disabling receiver Fl and transmitter F2 and for enabling receiver F2 and transmitter Fl and for causing said F1 transmitter to transmit a second signal so long as said signal is being produced, and third connections responsive to the removal of said instrument from said support, for maintaining said F1 receiver and F2 transmitter disabled and said F2 receiver and F1 transmitter enabled after said first-mentioned signal has been interrupted and so long as said instrument remains removed from said support.

5 A communication set comprising an instrucment for effecting a conversion between sound and electric energy, a support for said instrument, a single side band receiver designed to operate at a frequency F1, another single side band receiver designed to operate at a frequency F2 which differs from F1, a single side band transmitter designed to operate at said frequency F1, another single side band transmitter designed to operate at said frequency F2, first connections for enabling said Fl receiver and said F2 transmitter, and disabling said F2 receiver and said F1 transmitter, second connections responsive to a locally produced signal, for disabling receiver Fl and transmitter F2 and for enabling receiver F2 and transmitter El and. for causing said F-l transmitter to transmit a secondv signal so long, as

said signal is being produced, and third connections responsive to-the removal of said instrument from said support, for maintaing said F1 receiver and transmitter disabled and said F2 receiver and F1 transmitter enabled after said first-mentioned signal has been interrupted and connecting said Fl transmitter to transmit sound impressed on said instrument, said F1 transmitter and F2 receiver being maintained enabled and said transmitter and F1 receiver disabled and said Fltransmitter being connected to transmit sound so long as said instrument remains removed fromsaid support.

6. A communioatienset including a first trans.- mitter designed to operate at a frequency F1, a second transmitter designed to operate ata frequency F2 which differs from the frequency F1,

a first receiver designed to operate at said irequency F1, a second receiver designed to operate at saidfrequency F2, standby connection enabling receiver Fl and transmitter F2 and disabling receiver F2 and transmitter Fl, additional connections for disabling receiver Fl andtransmitter F2v and enabling receiver F2 and transmitter Fl, local manually operable means for causing said additional connections to disable receiver Fl and" transmitter F2 and to enable receiver F2 and transmitter Fl, and circuit means connectedto receiver Fl for causin said additional connections to respond to a signal received by receiver Fl from a remote point to maintain said receiver Fl and transmitter F2 enabled and receiver F2. and transmitter Fl disabled at least for a pre' determined time interval independently of the,

operation. of said manually operable means.

7. A communication set including, ajfirsttrans mitter designed to operate at a frequency Fl, a.v second transmitter designed to operate at a 'frequency F2 which differs from the frequency Fl,

a first receiver designed to operate at said fre-. quency F1, a second receiver designed to operate' at said frequency F2, stand-by connections en-,

abling receiver Fl and transmitter F2 and disabling receiver F2 and transmitter Fl, first connections for disabling receiver Fl and transmitter F2 and for enabling receiver F2 and transmitter ;Fl, means responsiveto a locally generated signal for causing said first connections to perform. said above-described disabling and enabling functions,

second connections for preventing said first connections from performing the above-described disabling and enabling operations and means re.-

sponsive to a signal received from a remote point before said locally enerated signal is produced for causing said second connections to perform its preventing operation.

a first receiver designed to operate at said frequency F1, a second receiver designed to operate at said frequency F2, stand-by connections enabling receiver Fl and transmitter F2 and dis-,

Fl, means responsive to a locally generatedsig-- na1 for. causing said first connections to performsaid above-described disabling and enabling. functions, second connections for preventing said I .first connections from performing thev abovee described disabling and enabling operations, said second connections including a timing mecha-.. nism for maintaining its above-described pre- I venting function for at leasta predetermined time intervalafter said remote signal has been interrupted, and-meansresponsive to a signal received from a remote pointbefore said locally-generated signal is'produced for causing said second connections to perform its preventing, operation for said time intervaL.

a receiver designed to operate at a frequency F1, another receiver designed to operate at a frequency F2'which differs from F1, a transmitter designedto operate at said frequency Fl', an-

other transmitter designed to operate atsaidfrequency F2, first connections for enabling said F1 receiver and said F2 transmitter and disabling said F2 receiver and said F1 transmitter, second connections for disabling receiver Fl and transmitter F2 and for enabling receiver F2 and transmitter Fl, means responsive to a locally produced signal for causing said first connections to perform its functions as aforesaid so long as said signal is being produced, third connections for maintaining said F1 receiver and F2 transmitter disabled and said F2 receiver and F1 transmitter enabled after said signal has been interrupted, means responsive to the removal of said instrument from said support for causing said third connections to perform said aforesaid functions so long as said instrument remains removed from said support, fourth connections for preventing the above-described functioning of said third connections, and means responsive to a signal received from a remote point when said signal is received prior to removal of said instrument from said support for causing said fourth connections to function as aforesaid.

10. A communication set comprising an instrument for effecting a conversion between sound and electric energy, a support for said instrument, a receiver designed to operate at a frequency F1, another receiver designed to operate at a frequency F2 which differs from F1, a transmitter designed to operate at said frequency F1. another transmitter designed to operate at said frequency F2, first connections for enabling said F1 receiver and said F2 transmitter and disabling said F2 receiver and said F1 transmitter, second connections for disabling receiver Fl and transmitter F2 and for enabling receiver F2 and transmitter Fl, means responsive to a locally produced signal for causing said second connections to function as aforesaid so long as said signal is being produced, third connections for maintaining said F1 receiver and F2 transmitter disabled and said F2 receiver and F1 transmitter enabled after said signal has been interrupted, means responsive to the removal of said instrument from said support for causing said third connections to function as aforesaid so long as said instrument remains removed from said support, fourth connections for preventing the above-described functioning of said third connections, said fourth connections including a timer for maintaining the abovedescribed functioning thereof for at least a predetermined interval after said remote signal has been interrupted, and means responsive to a signal received from a remote point if said signal is received prior to removal of said instrument from said support for causing said fourth connections to function as aforesaid for said interval.

11. A communication set comprising an instrument for effecting a conversion between sound and electric energy, a support for said instrument, a receiver designed to operate at a frequency F1, another receiver designed to operate at a frequency F2 which differs from F1, a transmitter designed to operate at said frequency F1, another transmitter designed to operate at said frequency F2, first connections for enabling said Fl receiver and said F2 transmitter and disabling said F2 receiver and said F1 transmitter, second connections for disabling receiver Fl and transmitter F2 and for enabling receiver F2 and transmitter Fl, means responsive to a locally produced signal for causing said second connections to function as aforesaid so long as said signal is being produced, third connections for maintaining said F1 receiver and F2 transmitter disabled and said F2 receiver and F1 transmitter enabled after said signal has 12 been interrupted, means responsive to the removal of said instrument from said support for causing said third connections to function as aforesaid so long as said instrument remains removed from said support, fourth connections for I preventing the above-described functioning of said third connections, said fourth connections including a timer for maintaining the above-described functioning thereof for at least a predetermined interval after said remote signal has been interrupted, means responsive to a signal received from a remote point when said signal is received prior to removal of said instrument from said support for causing said fourth connections to function as aforesaid for said interval, an indicator, fifth connections for actuating said indicator and means responsive to receipt of said remote signal for causing said fifth connections to function as aforesaid.

12. Communication apparatus comprising a first station having a first receiver designed to operate at frequency F1 and a first receiver designed to operate at frequency F2, which differs from F1, and a first transmitter designed to operate at said frequency F1 and first transmitter designed to operate at said frequency F2;

a second station having a second F1 receiver, a

a second F2 receiver, a second F1 transmitter and a second F2 transmitter; connection at each said stations enabling said first and second Fl receivers and said first and second F2 transmitters and disabling said first and second F2 receivers and said first and second F1 transmitters; a first locally actuable circuit at said first station responsive to a locally produced first signal for disabling said first Fl receiver and said first F2 transmitter and enabling said first F2 receiver and said first F1 transmitter'and for transmitting a second signal over said first F1 transmitter; a second locally actuable circuit at said second station responsive to a locally produced third signal for disabling said second F1 receiver and said second F2 transmitter and enabling said second F2 receiver and said second F1 transmitter and for transmitting a fourth signal over said second F1 transmitter; a first remotely actuable circuit at said first station responsive to reception of said fourth signal for preventing actuation of said first locally actuable circuit; and a second remotely actuable circuit at said second station responsive to reception of said second signal for preventing actuation of said first locally actuable circuit.

13. Communication apparatus comprising a first station having a first receiver designed to operate at frequency F1 and a first receiver designed to operate at frequency F2, which differs from F1, and a first transmitter designed to operate at said frequency F1 and first transmitter designed to operate at said frequency F2; a second station having a second F1 receiver, a second F2 receiver, a second F1 transmitter and a second F2 transmitter; connections at each said stations enabling said first and second F1 receivers and said first and second F2 transmitters and disabling said first and second F2 receivers and said first and a second F1 transmitters; a first locally actuable circuit at said first station responsive to a locally produced first signal for disabling said first F1 receiver and said first F2 transmitter and enabling said first F2 receiver and said first Fl transmitter and for transmitting a second signal over said first F1 transmitter; a second locally actuable circuit at said second station responsive 13 to a locally produced third signal for disabling said second F1 receiver and said second F2 transmitter and enabling said second F2 receiver and said second F1 transmitter and for transmitting a fourth signal over said second F1 transmitter; a first remotely actuable circuit at said first station responsive to reception of said fourth signal for preventing actuation of said first locally actuable circuit; for at least a predetermined time interval after receipt of said fourth signal has stopped, and a second remotely actuable circuit at said second station responsive to reception of said second signal for preventing actuation of said first locally actuable circuit for at least a predetermined time interval after receipt of said second signal has stopped.

14. Communication apparatus comprising a first station having a first receiver designed to operate at frequency F1 and a first receiver designed to operate at frequency F2, which differs from F1, and a first transmitter designed to operate at said frequency F1 and first transmitter designed to operate at said frequency F2; a second station having a second F1 receiver, a second F2 receiver, a second F1 transmitter and a second F2 transmitter; connections at each said stations enabling said first and second F1 receivers and said first and second F2 transmitters and disabling said first and second F2 receivers and said first and second F1 transmitters; a first locally actuable circuit at said first station responsive to a locally produced first signal both for disabling said first F1 receiver and said first F2 transmitter and enabling said first F2 receiver and said first Fl transmitter and for transmitting a second signal over said first F1 transmitter corresponding to said locally produced first signal; a second locally actuable circuit at said second station responsive to a locally produced third signal both for disabling said second F1 receiver and said second F2 transmitter and enabling said second F2 receiver and said second F1 transmitter and for transmitting a fourth signal over said second F1 transmitter corresponding to said locally produced third signal; a first remotely actuable circuit at said first station responsive to reception of said fourth signal for preventing actuation of said first locally actuable circuit; and a second remotely actuable circuit at said second station responsive to reception of said second signal for preventing actuation of said first locally actuable circuit.

15. A communication set including a first transmitter designed to operate at a frequency F1, a second transmitter designed to operate at a frequency F2 which differs from F1, a first receiver designed to operate at said F1 frequency. a second receiver designed to operate at said F2 frequency, stand-by connections enabling transmitter F2 and receiver Fl and disablin transmitter Fl and receiver F2, means for generating locally a signal having a predetermined characteristic and means responsive to said locally generated signal both for disabling transmitter F2 and receiver Fl and enabling transmitter Fl and receiver F2 and for transmitting a signal at frequency F1 having said predetermined characteristic.

16. In combination a first relay device; a second relay device; a timer, first terminals for connection to a power supply; a first circuit including said timer and said terminals adapted to be maintained closed by said relay devices only when both are in an unactuated state and to cause said timer to produce a timing operation; second terminals for connection to a power supply; a second circuit including said second terminals and said first relay device, said second circuit including means adapted to be closed by said timer when it performs a timing operation for actuating said first relay device; means for maintaining said first relay device actuated, once it is actuated, independently of said timer; mean for actuating said second relay device; and means responsive to said second relay device when it is actuated for interrupting the operation of said maintaining means.

ROBERT C. CHEEK. PAUL L. NEWBURY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,773,613 Clark Aug. 19, 1930. 2,264,397 Moore Dec. 2, 1941 2,289,048 Sandalls July 7, 1942 2,294,905 Honoman Sept. 8, 1942 2,430,471 Lang Nov. 11, 1947 2,440,239 Almquist Apr. 27, 1948 2,481,915 Edson Sept. 13, 1949 2,484,211 Emling Oct. 11, 1949 2,507,116 Moore .i May 9, 1950 2,511,615 Barstow et al. June 13, 1950 2,511,616 Barstow et al June 13, 1950 2,511,617 Barstow June 13, 1950 

